A Novel Diterpenoid Suppresses Osteoclastogenesis and Promotes Osteogenesis by Inhibiting Ifrd1-Mediated and IκBα-Mediated p65 Nuclear Translocation

Regulation of bone homeostasis by traditional Chinese medicine active scaffolds and enhancement for the osteoporosis bone regeneration

ETHNOPHARMACOLOGICAL RELEVANCE

The active ingredients of traditional Chinese medicine (TCM), such as naringin (NG), Eucommiol, isopsoralen, icariin, Astragalus polysaccharides, and chondroitin sulfate, contained in Drynariae Rhizoma, Eucommiae Cortex, Psoralea corylifolia, Herba Epimedii, Astragalus radix and deer antler, are considered promising candidates for enhancing the healing of osteoporotic defects due to their outstanding bone homeostasis regulating properties. They are commonly used to activate bone repair scaffolds.

AIM OF THE REVIEW

Bone repair scaffolds are inadequate to meet the demands of osteoporotic defect healing due to the lack of regulation of bone homeostasis. Therefore, selecting bone scaffolds activated with TCM to improve the therapeutic effect of repairing osteoporotic bone defects.

MATERIALS AND METHODS

To gather information on bone scaffold activated by traditional Chinese medicine, we conducted a thorough search of several scientific databases, including Google Scholar, Web of Science, Scifinder, Baidu Scholar, PubMed, and China National Knowledge Infrastructure (CNKI).

RESULTS

This review discusses the mechanism of TCM active ingredients in regulating bone homeostasis, including stimulating bone formation and inhibiting bone resorption process and the healing mechanism of traditional bone repair scaffolds activated by them for osteoporotic defect healing.

CONCLUSION

In general, the introduction of TCM active ingredients provides a novel therapeutic approach for modulating bone homeostasis and facilitating osteoporotic defect healing, and also offers a new strategy for design of other unconventional bone defect healing materials.

l-arginine promotes angio-osteogenesis to enhance oxidative stress-inhibited bone formation by ameliorating mitophagy

Background

Osteoporosis is one of the most common bone diseases in middle-aged and elderly populations worldwide. The development of new drugs to treat the disease is a key focus of research. Current treatments for osteoporosis are mainly directed at promoting osteoblasts and inhibiting osteoclasts. However, there is currently no ideal approach for osteoporosis treatment. l-arginine is a semi-essential amino acid involved in a number of cellular processes, including nitric production, protein biosynthesis, and immune responses. We previously reported that l-arginine-derived compounds can play a regulatory role in bone homeostasis.

Purpose

To investigate the specific effect of l-arginine on bone homeostasis.

Methods

Mildly aged and ovariectomized mouse models were used to study the effects of l-arginine on osteogenesis and angiogenesis, assessed by micro-computed tomography and immunostaining of bone tissue. The effect of l-arginine on osteogenesis, angiogenesis, and adipogenesis was further studied in vitro using osteoblasts obtained from cranial cap bone, endothelial cells, and an adipogenic cell line. Specific methods to assess these processes included lipid staining, cell migration, tube-forming, and wound-healing assays. Protein and mRNA expression was determined for select biomarkers.

Results

We found that l-arginine attenuated bone loss and promoted osteogenesis and angiogenesis. l-arginine increased the activity of vascular endothelial cells, whereas it inhibited adipogenesis in vitro. In addition, we found that l-arginine altered the expression of PINK1/Parkin and Bnip3 in the mitochondria of osteoblast-lineage and endothelial cells, thereby promoting mitophagy and protecting cells from ROS. Similarly, l-arginine treatment effectively ameliorated osteoporosis in an ovariectomized mouse model.

Conclusion

l-arginine promotes angio-osteogenesis, and inhibits adipogenesis, effects mediated by the PINK1/Parkin- and Bnip3-mediated mitophagy.

The Translational Potential of this Article

L-arginine supplementation may be an effective adjunct therapy in the treatment of osteoporosis.

Dlk2 interacts with Syap1 to activate Akt signaling pathway during osteoclast formation

Excessive osteoclast formation and bone resorption are related to osteolytic diseases. Delta drosophila homolog-like 2 (Dlk2), a member of the epidermal growth factor (EGF)-like superfamily, reportedly regulates adipocyte differentiation, but its roles in bone homeostasis are unclear. In this study, we demonstrated that Dlk2 deletion in osteoclasts significantly inhibited osteoclast formation in vitro and contributed to a high-bone-mass phenotype in vivo. Importantly, Dlk2 was shown to interact with synapse-associated protein 1 (Syap1), which regulates Akt phosphorylation at Ser473. Dlk2 deletion inhibited Syap1-mediated activation of the AktSer473, ERK1/2 and p38 signaling cascades. Additionally, Dlk2 deficiency exhibits increased bone mass in ovariectomized mice. Our results reveal the important roles of the Dlk2-Syap1 signaling pathway in osteoclast differentiation and osteoclast-related bone disorders.

SIRT2 regulates extracellular vesicle-mediated liver-bone communication

The interplay between liver and bone metabolism remains largely uncharacterized. Here, we uncover a mechanism of liver-bone crosstalk regulated by hepatocyte SIRT2. We demonstrate that hepatocyte SIRT2 expression is increased in aged mice and elderly humans. Liver-specific SIRT2 deficiency inhibits osteoclastogenesis and alleviates bone loss in mouse models of osteoporosis. We identify leucine-rich α-2-glycoprotein 1 (LRG1) as a functional cargo in hepatocyte-derived small extracellular vesicles (sEVs). In SIRT2-deficient hepatocytes, LRG1 levels in sEVs are upregulated, leading to increased transfer of LRG1 to bone-marrow-derived monocytes (BMDMs), and in turn, to inhibition of osteoclast differentiation via reduced nuclear translocation of NF-κB p65. Treatment with sEVs carrying high levels of LRG1 inhibits osteoclast differentiation in human BMDMs and in mice with osteoporosis, resulting in attenuated bone loss in mice. Furthermore, the plasma level of sEVs carrying LRG1 is positively correlated with bone mineral density in humans. Thus, drugs targeting hepatocyte-osteoclast communication may constitute a promising therapeutic strategy for primary osteoporosis.

Oridonin Attenuates Thioacetamide-Induced Osteoclastogenesis Through MAPK/NF-κB Pathway and Thioacetamide-Inhibited Osteoblastogenesis Through BMP-2/RUNX2 Pathway

Osteoporosis, an age-related metabolic bone disease, is mainly caused by an imbalance between osteoblast-mediated bone formation and osteoclast-mediated bone resorption. At present, there are many osteoporosis drugs that can promote bone formation or inhibit bone resorption. However, there were few therapeutic drugs that can simultaneously promote bone formation and inhibit bone resorption. Oridonin (ORI), a tetracyclic diterpenoid compound isolated from Rabdosia rubescens, has been proved to have anti-inflammatory, anti-tumor effects. However, little is known about the osteoprotective effect of oridonin. Thioacetamide (TAA) is a common organic compound with significant hepatotoxicity. Recent studies have found that there was a certain association between TAA and bone injury. In this work, we investigated the effect and mechanism of ORI on TAA-induced osteoclastogenesis and inhibition of osteoblast differentiation. The results showed that TAA could promote the osteoclastogenesis of RAW264.7 by promoting the MAPK/NF-κB pathway, and also promoted p65 nuclear translocation and activated intracellular ROS generation, and ORI can inhibit these effects to inhibit TAA-induced osteoclastogenesis. Moreover, ORI can also promote the osteogenic differentiation pathway and inhibit adipogenic differentiation of BMSCs to promote bone formation. In conclusion, our results revealed that ORI, as a potential therapeutic drug for osteoporosis, could protect against TAA-induced bone loss and TAA-inhibited bone formation.

A Novel Inhibitor INF 39 Promotes Osteogenesis via Blocking the NLRP3/IL-1β Axis

Purpose. A balance between osteoblasts and osteoclasts is essential to maintain skeletal integrity, regulating bone metabolism and bone remodeling. The nucleotide binding oligomerization domain, leucine-rich repeat and pyrin domain containing protein 3 (NLRP3) inflammasome is known as a cytosolic complex involved in producing proinflammatory cytokines consisting of interleukin- (IL-) 1β, which accelerates the occurrence of osteoporosis. Therefore, we aimed to investigate the effect of a novel NLRP3 inhibitor INF 39 on bone formation and bone resorption. Material and Methods. Cell viability of INF 39-treated osteoclasts and calvarial osteoblasts was tested by CCK-8 assays. Quantitative RT-PCR (qRT-PCR) was used to evaluate gene expression level during osteoblast and osteoclast formation. Western blot analysis was used to determine the effect of INF 39 on osteogenic and osteoclast-related proteins. Result. It was shown that INF 39 promotes osteoblast differentiation via inhibiting NLRP3, thereby reducing the production of IL-1β dependent on NLRP3 in vitro. However, RANKL-induced osteoclast differentiation is not influenced by INF 39 in vitro. Conclusion. Our study suggests that NLRP3 could be a new target and INF 39 may be a potential option for prevention and treatment of osteoporosis.

Tereticornate A suppresses RANKL-induced osteoclastogenesis via the downregulation of c-Src and TRAF6 and the inhibition of RANK signaling pathways

Excessive osteoclast differentiation and activation are closely associated with the development and progression of osteoporosis. Natural plant-derived compounds that can inhibit osteoclastogenesis are an efficient strategy for the prevention and treatment of osteoporosis. Tereticornate A (TA) is a natural terpene ester compound extracted from the leaves and branches of Eucalyptus gracilis, with antiviral, antibacterial, and anti-inflammatory activities. However, the effect of TA on osteoclastogenesis and the underlying molecular mechanism remain unclear. Based on the key role of the NF-κB pathway in the regulation of osteoclastogenesis and the observation that TA exhibits an anti-inflammatory effect by inhibiting NF-κB activity, we speculated that TA could exert anti-osteoclastogenesis activity. Herein, TA could inhibit the RANKL-induced osteoclast differentiation and formation of F-actin rings in RAW 264.7 cells. Mechanistically, TA downregulated the expression of c-Src and TRAF6, and also suppressed the RANKL-stimulated canonical RANK signaling pathways, including AKT, MAPK (p38, JNK, and ERK), and NF-κB; ultimately, downregulating the expression of NFATc1 and c-Fos, the key transcriptional factors required for the expression of genes (e.g., TRAP, cathepsin K, β-Integrin, MMP-9, ATP6V0D2, and DC-STAMP) that govern osteoclastogenesis. Our findings demonstrated that TA could effectively inhibit RANKL-induced osteoclastogenesis via the downregulation of c-Src and TRAF6 and the inhibition of RANK signaling pathways. Thus, TA could serve as a novel osteoclastogenesis inhibitor and might have beneficial effects on bone health.

Phillyrin Prevents Ovariectomy-Induced Osteolysis by Inhibiting Osteoclast Differentiation

Postmenopausal osteoporosis is a metabolic disease caused by an imbalance between osteoclasts and osteoblasts. At present, the drug strategy for treating postmenopausal osteoporosis has some limitations and is unable to satisfy the demands of patients. Phillyrin (Phil) is an herbal extract from Forsythiae Fructus, with an inhibitory effect on osteolysis. In this study, we described the role of Phil in ovariectomy-induced osteoporosis and its effect on osteoclast differentiation in vitro. Eighteen female C57BL/6 mice were randomly divided into three groups: sham group (sham surgery and injection with 0.9% normal saline), ovariectomized group (ovariectomy and injection with 0.9% normal saline), and Phil group (ovariectomy and injecting Phil with 100 mg/kg for 2 days). Mice were sacrificed after 6-week Phil administration and femurs were harvested for microcomputed tomography (micro-CT) and histomorphology analyses. In vitro, we used different concentrations of Phil to study its effect on osteoclastogenesis. The results showed that the BV/TV, Tb.Th, and Tb.N in trabecular bone were increased in the Phil group compared with the OVX group, and the trabecular bone mass was remarkably decreased in the OVX group compared with the sham group. The number of osteoclasts was increased in the OVX group compared to the sham group, and the number and area of osteoclasts were decreased in the Phil group compared to the control group. Compared with the OVX group, the number and area of osteoclasts were reduced in the Phil group. In conclusion, Phil could inhibit the formation of osteoclasts, promote the growth of bone trabecular, and relieve osteoporosis caused by ovariectomy, with a certain clinical adoption value.

The SFRP1 Inhibitor WAY-316606 Attenuates Osteoclastogenesis Through Dual Modulation of Canonical Wnt Signaling

Osteoporosis, a noteworthy age-related disease induced by imbalanced osteogenesis and osteoclastogenesis, is a serious economic burden on both individuals and society. Small molecule drugs with dual effects on both bone resorption and mineralization are pressingly needed. Secreted frizzled-related protein 1 (SFRP1), a well-known extracellular repressor of canonical Wnt signaling, has been reported to regulate osteogenesis. Global SFRP1 knockout mice show significantly elevated bone mass. Although osteoclasts (OCs) express and secrete SFRP1, the role of SFRP1 produced by OCs in osteoclastogenesis and osteoporosis remains unclear. In this work, the levels of SFRP1 were found to be increased in patients with osteoporosis compared with healthy controls. Pharmacological inhibition of SFRP1 by WAY-316606 (WAY)- attenuated osteoclastogenesis and bone resorption in vitro. The expressions of OC-specific genes were suppressed by the SFRP1 inhibitor, WAY. Mechanistically, both extracellular and intracellular SFRP1 could block activation of the canonical Wnt signaling pathway, and WAY reverse the silent status of canonical Wnt through dual effects, leading to osteoclastogenesis inhibition and osteogenesis promotion. Severe osteopenia was observed in the ovariectomized (OVX) mouse model, and WAY treatment effectively improved the OVX-induced osteoporosis. In summary, this work found that SFRP1 supports OC differentiation and function, which could be attenuated by WAY through dual modulation of canonical Wnt signaling, suggesting its therapeutic potential. © 2021 American Society for Bone and Mineral Research (ASBMR).

Evolving Roles of Natural Terpenoids From Traditional Chinese Medicine in the Treatment of Osteoporosis

Osteoporosis (OP) is a systemic metabolic skeletal disease which can lead to reduction in bone mass and increased risk of bone fracture due to the microstructural degradation. Traditional Chinese medicine (TCM) has been applied in the prevention and treatment of osteoporosis for a long time. Terpenoids, a class of natural products that are rich in TCM, have been widely studied for their therapeutic efficacy on bone resorption, osteogenesis, and concomitant inflammation. Terpenoids can be classified in four categories by structures, monoterpenoids, sesquiterpenoids, diterpenoids, and triterpenoids. In this review, we comprehensively summarize all the currently known TCM-derived terpenoids in the treatment of OP. In addition, we discuss the possible mechanistic-of-actions of all four category terpenoids in anti-OP and assess their therapeutic potential for OP treatment.

DZNep promotes mouse bone defect healing via enhancing both osteogenesis and osteoclastogenesis

Background

Enhancer of zeste homolog 2 (EZH2) is a novel oncogene that can specifically trimethylate the histone H3 lysine 27 (H3K27me3) to transcriptionally inhibit the expression of downstream tumor-suppressing genes. As a small molecular inhibitor of EZH2, 3-Deazaneplanocin (DZNep) has been widely studied due to the role of tumor suppression. With the roles of epigenetic regulation of bone cells emerged in past decades, the property and molecular mechanism of DZNep on enhancing osteogenesis had been reported and attracted a great deal of attention recently. This study aims to elucidate the role of DZNep on EZH2-H3K27me3 axis and downstream factors during both osteoclasts and osteoblasts formation and the therapeutic possibility of DZNep on bone defect healing.

Methods

Bone marrow-derived macrophages (BMMs) cells were cultured, and their responsiveness to DZNep was evaluated by cell counting kit-8, TRAP staining assay, bone resorption assay, podosome actin belt. Bone marrow-derived mesenchymal stem cells (BMSC) were cultured and their responsiveness to DZNep was evaluated by cell counting kit-8, ALP and AR staining assay. The expression of nuclear factor-κB (NF-κB), mitogen-activated protein kinase (MAPK), Wnt signaling pathway was determined by qPCR and western blotting. Mouse bone defect models were created, rescued by DZNep injection, and the effectiveness was evaluated by X-ray and micro-CT and histological staining.

Results

Consistent with the previous study that DZNep enhances osteogenesis via Wnt family member 1(Wnt1), Wnt6, and Wnt10a, our results showed that DZNep also promotes osteoblasts differentiation and mineralization through the EZH2-H3K27me3-Wnt4 axis. Furthermore, we identified that DZNep promoted the receptor activator of nuclear factor-κB (NF-κB) ligand (RANKL)-induced osteoclast formation via facilitating the phosphorylation of IKKα/β, IκB, and subsequently NF-κB nuclear translocation, which credit to the EZH2-H3K27me3-Foxc1 axis. More importantly, the enhanced osteogenesis and osteoclastogenesis result in accelerated mice bone defect healing in vivo.

Conclusion

DZNep targeting EZH2-H3K27me3 axis facilitated the healing of mice bone defect via simultaneously enhancing osteoclastic bone resorption and promoting osteoblastic bone formation.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-021-02670-6.

Nitazoxanide, an Antiprotozoal Drug, Reduces Bone Loss in Ovariectomized Mice by Inhibition of RANKL-Induced Osteoclastogenesis

Nitazoxanide (NTZ) is an FDA-approved anti-parasitic drug with broad-spectrum anti-infective, anti-inflammatory, and antineoplastic potential. However, its regulatory effects on osteoclastogenesis and the underlying mechanisms remain unclear. The present study found that NTZ potently inhibited osteoclast formation at the early stage of receptor activator of NF-κB ligand-induced osteoclastogenesis in a concentration-dependent manner at a non-growth inhibitory concentration. NTZ suppressed actin ring formation and decreased osteoclast marker gene expression, including TRAP, MMP9, and cathepsin K. NTZ significantly impaired the bone resorption activity of osteoclasts. In vivo, ovariectomized mice were treated with 50, 100 and 200 mg/kg/d NTZ for 3 months. NTZ (100 mg/kg/d) administration markedly reduced ovariectomy-induced bone loss by suppressing osteoclast activity. Mechanistically, osteoclastogenesis blockade elicited by NTZ resulted from inhibition of STAT3 phosphorylation, and reduction of the Ca2+ fluorescence intensity and NFATc1 expression. NTZ weakened the binding between STAT3 and the NFATc1 promoter region. Furthermore, enforced NFATc1 expression partly rescued the impaired osteoclast differentiation in NTZ-treated RAW264.7 cells. In summary, NTZ could inhibit osteoclastogenesis and bone loss through modulation of the receptor activator of NF-κB ligand-induced STAT3-NFATc1 signaling pathway, which might be a potential alternative treatment regimen against bone destruction-related diseases including osteoporosis.

Nicorandil Inhibits Osteoclast Formation Base on NF-κB and p-38 MAPK Signaling Pathways and Relieves Ovariectomy-Induced Bone Loss

Osteolytic bone disorders are characterized by an overall reduction in bone mineral density which enhances bone ductility and vulnerability to fractures. This disorder is primarily associated with superabundant osteoclast formation and bone resorption activity. Nicorandil (NIC) is a vasodilatory anti-anginal drug with ATP-dependent potassium (KATP) channel openings. However, NIC is adopted to manage adverse cardiovascular and coronary events. Recent research has demonstrated that NIC also possesses anti-inflammatory peculiarity through the regulation of p38 MAPK and NF-κB signaling pathways. Both MAPK and NF-κB signaling pathways play pivotal roles in RANKL-induced osteoclast formation and bone resorption function. Herein, we hypothesized that NIC may exert potential biological effects against osteoclasts, and revealed that NIC dose-dependently suppressed bone marrow macrophage (BMM) precursors to differentiate into TRAP + multinucleated osteoclasts in vitro. Furthermore, osteoclast resorption assays demonstrated anti-resorptive effects exhibited by NIC. NIC had no impact on osteoblast differentiation or mineralization function. Based on Biochemical analyses, NIC relieved RANKL-induced ERK, NF-κB and p38 MAPK signaling without noticeable effects on JNK MAPK activation. However, the attenuation of NF-κB and p38 MAPK activation was sufficient to hamper the downstream induction of c-Fos and NFATc1 expression. Meanwhile, NIC administration markedly protected mice from ovariectomy (OVX)-induced bone loss through in vivo inhibition of osteoclast formation and bone resorption activity. Collectively, this work demonstrated the potential of NIC in the management of osteolytic bone disorders mediated by osteoclasts.

Oxidative Stress-Induced Hypermethylation of KLF5 Promoter Mediated by DNMT3B Impairs Osteogenesis by Diminishing the Interaction with β-Catenin

Aims: Emerging evidence suggests that the pathogenesis of osteoporosis, characterized by impaired osteogenesis, is shifting from estrogen centric to oxidative stress. Our previous studies have shown that the zinc-finger transcription factor krüppel-like factor 5 (KLF5) plays a key role in the degeneration of nucleus pulposus and cartilage. However, its role in osteoporosis remains unknown. We aimed to investigate the effect and mechanism of KLF5 on osteogenesis under oxidative stress. Results: First, KLF5 was required for osteogenesis and stimulated osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs). KLF5 was hypermethylated and downregulated in ovariectomy-induced osteoporosis mice and in BMSCs treated with H2O2. Interestingly, DNA methyltransferases 3B (DNMT3B) upregulation mediated the hypermethylation of KLF5 induced by oxidative stress, thereby impairing osteogenic differentiation. The inhibition of KLF5 hypermethylation using DNMT3B siRNA or 5-AZA-2-deoxycytidine (5-AZA) protected osteogenic differentiation of BMSCs from oxidative stress. Regarding the downstream mechanism, KLF5 induced β-catenin expression. More importantly, KLF5 promoted the nuclear translocation of β-catenin, which was mediated by the armadillo repeat region of β-catenin. Consistently, oxidative stress-induced KLF5 hypermethylation inhibited osteogenic differentiation by reducing the expression and nuclear translocation of β-catenin. Innovation: We describe the novel effect and mechanism of KLF5 on osteogenesis under oxidative stress, which is linked to osteoporosis for the first time. Conclusion: Our results suggested that oxidative stress-induced hypermethylation of KLF5 mediated by DNMT3B impairs osteogenesis by diminishing the interaction with β-catenin, which is likely to contribute to osteoporosis. Targeting the hypermethylation of KLF5 might be a new strategy for the treatment of osteoporosis. Antioxid. Redox Signal. 35, 1-20.

Hinokitiol inhibits RANKL-induced osteoclastogenesis in vitro and prevents ovariectomy-induced bone loss in vivo

Osteoporosis is a metabolic bone-loss disease characterized by abnormally excessive osteoclast formation and bone resorption. Identification of natural medicines that can inhibit osteoclastogenesis, bone resorption, and receptor activator of nuclear factor-κB ligand (RANKL)-induced signaling is necessary for improved treatment of osteoporosis. In this study, hinokitiol, a tropolone-related compound extracted from the heart wood of several cupressaceous plants, was found to inhibit RANKL-induced osteoclast formation and bone resorption in vitro. Hinokitiol inhibited early activation of the ERK, p38, and JNK-MAPK pathways, thereby suppressing the activity and expression of downstream factors (c-Jun, c-Fos, and NFATC1). Consistent with the above in vitro findings, hinokitiol treatment protected against ovariectomy-induced bone loss in vivo. Collectively, our results imply that hinokitiol can potentially serve as an effective agent for treating osteoclast-induced osteoporosis.

Site-1 protease controls osteoclastogenesis by mediating LC3 transcription

Site-1 protease (S1P) is a Golgi-located protein that activates unique membrane-bound latent transcription factors, and it plays an indispensable role in endoplasmic reticulum stress, lipid metabolism, inflammatory response and lysosome function. A patient with S1P mutation exhibits severe skeletal dysplasia with kyphoscoliosis, dysmorphic facial features and pectus carinatum. However, whether S1P regulates bone remodeling by affecting osteoclastogenesis remains elusive. Here, we show that S1P is indeed a positive regulator of osteoclastogenesis. S1P ablation in mice led to significant osteosclerosis compared with wild-type littermates. Mechanistically, S1P showed upregulated during osteoclastogenesis and was identified as a direct target of miR-9-5p. S1P deletion in bone marrow monocytes (BMMs) inhibited ATF6 and SREBP2 maturation, which subsequently impeded CHOP/SREBP2-complex-induced LC3 expression and autophagy flux. Consistently, transfection of LC3 adenovirus evidently rescued osteoclastogenesis in S1P-deficient BMMs. We then identified the interaction regions between CHOP and SREBP2 by Co-immunoprecipitation (Co-IP) and molecular docking. Furthermore, S1P deletion or inhibitor efficaciously rescued ovariectomized (OVX)- and LPS-induced bone loss in vivo. Collectively, we showed that S1P regulates osteoclast differentiation in a LC3 dependent manner and so is a potential therapy target for osteoporosis.

Oxymatrine Attenuates Osteoclastogenesis via Modulation of ROS-Mediated SREBP2 Signaling and Counteracts Ovariectomy-Induced Osteoporosis

Osteoporosis, mainly caused by osteoclast-induced bone resorption, has become a major health problem in post-menopausal women and the elderly. Growing evidence indicates that inhibiting osteoclastogenesis is an efficient approach to develop alternative therapeutic agents for treating osteoporosis. In this study, we identified the potential regulating role of Oxymatrine (OMT), a quinazine alkaloid extracted from Sophora flavescens with various therapeutic effects in many diseases, on osteoclastogenesis for the first time. We found that OMT attenuated RANKL-induced osteoclast formation in both time- and dose-dependent manners. Further, OMT significantly suppressed RANKL-induced sterol regulatory element-binding protein 2 (SREBP2) activation and the expression of the nuclear factor of activated T cells 1 (NFATc1). Moreover, OMT inhibited the generation of RANKL-induced reactive oxygen species (ROS), and the upregulation of ROS could rescue the inhibition of SREBP2 by OMT. More importantly, ovariectomy (OVX) mouse model showed that OMT could effectively improve ovariectomy (OVX)-induced osteopenia by inhibiting osteoclastogenesis in vivo. In conclusion, our data demonstrated that OMT impaired ROS mediated SREBP2 activity and downstream NFATc1 expression during osteoclastogenesis, suppressed OVX-induced osteopenia in vivo, which suggested that OMT could be a promising compound for medical treatment against osteoporosis.

Hepatoprotective effects of oridonin against bisphenol A induced liver injury in rats via inhibiting the activity of xanthione oxidase

Bisphenol A (BPA) is widely used to manufacture packaging materials for various daily necessities and causes harmful effects in organs, especially liver injury, by generating oxidative stress. Oridonin, an active diterpenoid isolated from Rabdosia rubescens (Hemsl.) Hara, has been reported to possess a wide range of pharmacological activities including anti-inflammatory, antioxidative and antiapoptotic effects. However, the role of oridonin in BPA--induced liver injury and its potential protective mechanism have not been well characterized. In this research, we explored the metabolic alterations in the liver tissue of rats after exposure to BPA with or without pretreatment with oridonin for 14 days by metabolomics analysis based on UPLC-MS/MS. Rats were randomly divided into groups as follows: Control, Vehicle, Oridonin (10 mg/kg), Bisphenol A (500 mg/kg), bisphenol A + Oridonin (500 + 10 mg/kg), Bisphenol A + Diammonium glycyrrhizinate (500 + 40 mg/kg). The biochemical results showed that oridonin significantly reduced the levels of AST and ALT (P < 0.05), ameliorated the abnormal histopathological changes and reduced hepatic apoptosis compared with the BPA group. Furthermore, metabolomics results revealed that purine metabolism, phenylalanine, tyrosine and tryptophan biosynthesis and phenylalanine metabolism were reprogrammed, based on 28 identified significant differential metabolites among the Vehicle, BPA and BPA + oridonin groups. In-depth studies demonstrated that pretreatment with oridonin may play a protective role by restoring BPA-induced changes in oxidative stress and the activity of oxidase (XOD) (P < 0.05). Additionally, oridonin could inhibit the activity of XOD by binding to it, therefore decreasing the reactive oxygen species (ROS) level, upregulating the content of hypoxanthine and xanthine, and reducing the level of uric acid in the liver (P < 0.05). This research presents the potential protective mechanisms of oridonin on BPA-induced liver injury at the metabolic level, which might be used to identify new protective agents that prevent BPA-induced liver injury.

Low-dose IL-34 has no effect on osteoclastogenesis but promotes osteogenesis of hBMSCs partly via activation of the PI3K/AKT and ERK signaling pathways

Background

Inflammatory microenvironment is significant to the differentiation and function of mesenchymal stem cells (MSCs). It evidentially influences the osteoblastogenesis of MSCs. IL-34, a newly discovered cytokine, playing a key role in metabolism. However, the research on its functional role in the osteogenesis of MSCs was rarely reported. Here, we described the regulatory effects of low-dose IL-34 on both osteoblastogenesis and osteoclastogenesis.

Methods

We performed the osteogenic effects of hBMSCs by exogenous and overexpressed IL-34 in vitro, so were the osteoclastogenesis effects of mBMMs by extracellular IL-34. CCK-8 was used to assess the effect of IL-34 on the viability of hBMSCs and mBMMs. ALP, ARS, and TRAP staining was used to evaluate ALP activity, mineral deposition, and osteoclastogenesis, respectively. qRT-PCR and Western blotting analysis were performed to detect the expression of target genes and proteins. ELISA was used to evaluate the concentrations of IL-34. In vivo, a rat tibial osteotomy model and an OVX model were established. Radiographic analysis and histological evaluation were performed to confirm the therapeutic effects of IL-34 in fracture healing and osteoporosis. Statistical differences were evaluated by two-tailed Student’s t test, one-way ANOVA with Bonferroni’s post hoc test, and two-way ANOVA with Bonferroni multiple comparisons post hoc test in the comparison of 2 groups, more than 2 groups, and different time points of treated groups, respectively.

Results

Promoted osteoblastogenesis of hBMSCs was observed after treated by exogenous or overexpressed IL-34 in vitro, confirmed by increased mineral deposits and ALP activity. Furthermore, exogenous or overexpressed IL-34 enhanced the expression of p-AKT and p-ERK. The specific AKT and ERK signaling pathway inhibitors suppressed the enhancement of osteoblastogenesis induced by IL-34. In a rat tibial osteotomy model, imaging and histological analyses testified the local injection of exogenous IL-34 improved bone healing. However, the additional IL-34 has no influence on both osteoclastogenesis of mBMMs in vitro and osteoporosis of OVX model of rat in vivo.

Conclusions

Collectively, our study demonstrate that low-dose IL-34 regulates osteogenesis of hBMSCs partly via the PIK/AKT and ERK signaling pathway and enhances fracture healing, with neither promoting nor preventing osteoclastogenesis in vitro and osteoporosis in vivo.

Oridonin ameliorates inflammation-induced bone loss in mice via suppressing DC-STAMP expression

Currently, dendritic cell-specific transmembrane protein (DC-STAMP), a multipass transmembrane protein, is considered as the master regulator of cell-cell fusion, which underlies the formation of functional multinucleated osteoclasts. Thus, DC-STAMP has become a promising target for osteoclast-associated osteolytic diseases. In this study, we investigated the effects of oridonin (ORI), a natural tetracyclic diterpenoid compound isolated from the traditional Chinese herb Rabdosia  rubescens, on osteoclastogenesis in vivo and ex vivo. ICR mice were injected with LPS (5 mg/kg, ip, on day 0 and day 4) to induce inflammatory bone destruction. Administration of ORI (2, 10 mg·kg^-1·d^-1, ig, for 8 days) dose dependently ameliorated inflammatory bone destruction and dramatically decreased DC-STAMP protein expression in BMMs isolated from LPS-treated mice. Treatment of preosteoclast RAW264.7 cells with ORI (0.78-3.125 μM) dose dependently inhibited both mRNA and protein levels of DC-STAMP, and suppressed the following activation of NFATc1 during osteoclastogenesis. Knockdown of DC-STAMP in RAW264.7 cells abolished the inhibitory effects of ORI on RANKL-induced NFATc1 activity and osteoclast formation. In conclusion, we show for the first time that ORI effectively attenuates inflammation-induced bone loss by suppressing DC-STAMP expression, suggesting that ORI is a potential agent against inflammatory bone diseases.

miR-21-5p targets SKP2 to reduce osteoclastogenesis in a mouse model of osteoporosis

Osteoporosis results from an imbalance between bone formation and bone resorption. Traditional drugs for treating osteoporosis are associated with serious side effects, and thus, new treatment methods are required. This study investigated the role of differentially expressed microRNAs during osteoclast differentiation and osteoclast activity during osteoarthritis as well as the associated underlying mechanisms. We used a microarray to screen microRNAs that decreased in the process of osteoclast differentiation and verified miR-21-5p to decrease significantly using RT-qPCR. In follow-up experiments, we found that miR-21-5p targets SKP2 to regulate osteoclast differentiation. In vivo, ovariectomized mice were used to simulate perimenopausal osteoporosis induced by estrogen deficiency, and miR-21-5p treatment inhibited bone resorption and maintained bone cortex and trabecular structure. These results suggest that miR-21-5p is a new therapeutic target for osteoporosis.

Bone Morphogenetic Protein-2 Promotes Osteoclasts-mediated Osteolysis via Smad1 and p65 Signaling Pathways

STUDY DESIGN

An in vitro biological study.

OBJECTIVE

The aim of this study was to explore the role of bone morphogenetic protein-2 (BMP-2) in the regulation of osteoclast-mediated osteolysis, and the possible mechanism involving BMP-2 and nuclear factor-kappa B (NF-κB) signaling pathways.

SUMMARY OF BACKGROUND DATA

Recombinant human BMP-2 (rhBMP-2) has been approved as a therapeutic agent in spinal fusion and bone defect repair. However, its efficacy and clinical application are limited by associated complications including osteoclast-mediated bone resorption. The mechanism of BMP-2-induced osteolysis remains unknown.

METHODS

Bone marrow-derived macrophages (BMMs) were isolated from C57BL/6J mice and cultured with macrophage colony-stimulating factor (M-CSF) and receptor activator for nuclear factor-κB Ligand (RANKL) to induce osteoclast differentiation. An in vitro bone resorption assay was performed by co-culturing BMMs and bone slides. The expression of BMP canonical and NF-κB signaling factors and their interaction during signal transduction were quantitated by reverse transcription polymerase chain reaction, Western blot analysis, confocal microscopy, and co-immunoprecipitation.

RESULTS

BMP-2 enhanced osteoclast-mediated bone resorption via inducing osteoclast differentiation in a concentration-dependent manner. In addition, a high concentration of BMP-2 significant upregulated phosphorylation of BMP signaling factors p-Smad1/5/8 and NF-κB downstream factor p65, and promoted the degeneration of IκBα. In addition, BMP-2 induced osteoclast differentiation through coupling between BMP receptor II and RANK.

CONCLUSION

High concentrations of BMP-2 enhanced osteoclast-mediated bone resorption by promoting RANKL-induced pre-osteoclast differentiation, probably by mediating the cross-talk between BMP canonical and NF-κB signaling pathways.Level of Evidence: N/A.

Recent Progress of Oridonin and Its Derivatives for the Treatment of Acute Myelogenous Leukemia

First stage human clinical trial (CTR20150246) for HAO472, the L-alanine-(14-oridonin) ester trifluoroacetate, was conducted by a Chinese company, Hengrui Medicine Co. Ltd, to develop a new treatment for acute myelogenous leukemia. Two patents, WO2015180549A1 and CN201410047904.X, covered the development of the I-type crystal, stability experiment, conversion rate research, bioavailability experiment, safety assessment, and solubility study. HAO472 hewed out new avenues to explore the therapeutic properties of oridonin derivatives and develop promising treatment of cancer originated from naturally derived drug candidates. Herein, we sought to overview recent progress of the synthetic, physiological, and pharmacological investigations of oridonin and its derivatives, aiming to disclose the therapeutic potentials and broaden the platform for the discovery of new anticancer drugs.

A selected small molecule prevents inflammatory osteolysis through restraining osteoclastogenesis by modulating PTEN activity

BACKGROUND

Inflammatory osteolysis is a severe infectious bone disorder that occurs during orthopaedic surgery and is caused by disruptions in the dynamic balance of bone matrix homeostasis, which makes this condition a burden on surgical procedures. Developing novel therapeutic drugs about inhibiting excessive osteoclastogenesis acts as an efficient approach to preventing inflammatory bone destruction.

METHODS

To study this, we explored the potential effects and mechanisms of compound 17 on inflammatory osteolysis in vitro. Meanwhile, a lipopolysaccharide (LPS)-induced calvarial osteolysis mouse model was used to evaluate the protective effect of compound 17 on inflammatory bone destruction in vivo.

RESULTS

In our study, we found that compound 17 could inhibit osteoclast (OC) differentiation and bone resorption during RANKL and LPS stimulation in a time- and dose-dependent manner, while compounds 5 and 13 did not have the same effects. Mechanistically, compound 17 promoted phosphatase and tensin homologue (PTEN) activity by reducing PTEN ubiquitination, thereby restraining the RANKL-induced NF-κB pathway, resulting in the inhibition of the expression of osteoclastogenesis-related genes and the formation of the NLRP3 inflammasome. Additionally, we also investigated whether compound 17 could negatively modulate macrophage polarization and repolarization due to its anti-inflammatory effects. Moreover, compound 17 also plays an important role in osteoblast differentiation and mineralization. In vivo experiments showed that compound 17 could effectively protect mice from LPS-induced inflammatory bone destruction by inhibiting osteoclastogenesis and inflammation.

CONCLUSIONS

Taken together, these results show that compound 17 might play protective role in inflammatory bone destruction through inhibiting osteoclastogenesis and inflammation. These findings imply a possible role of compound 17 in inflammatory osteolysis-related diseases.

Oridonin promotes osteogenesis through Wnt/β-catenin pathway and inhibits RANKL-induced osteoclastogenesis in vitro

AIMS

To study the molecular mechanism of oridonin (ORI) on osteoblast differentiation and osteoclast formation in vitro.

MAIN METHODS

Rat bone marrow mesenchymal stem cells (BMSCs) were treated with different concentrations of ORI in osteogenic medium (OM). CCK-8 assay and were used to detect the effect on BMSCs viability. Alizarin red staining and ALP activity were used to illuminate the effect of ORI on osteogenic differentiation. Expressions of osteogenic differentiation related genes were detected by real-time quantitative PCR (qRT-PCR), and expressions of osteogenic related proteins were detected by Western blot (WB) and immunofluorescence. Similarly, bone marrow mononuclear cells (BMMs) were treated with different concentrations of ORI. CCK-8 assay and Live/Dead staining were used to detect the effect of ORI on BMMs activity. TRAP staining was used to detect its effect on osteoclast differentiation. Expressions of osteoclast-related genes were detected by qRT-PCR, and expressions of osteoclast-related proteins were detected by WB and immunofluorescence.

KEY FINDINGS

(1) ORI (2 μM) promoted the ALP activity of BMSCs differentiation into osteoblasts and increased the number of calcium nodules. (2) ORI stimulated the expressions of wnt1, β-catenin and Runx2, but with no significantly effect on p-GSK-3β and GSK-3β. (3) ORI promoted the expression of OPG and inhibited the expression of RANKL. (4) ORI directly/indirectly inhibited the osteoclast formation and expressions of osteoclast-related genes TRAP, NFATc1 and c-Fos.

SIGNIFICANCE

ORI may promote BMSCs differentiate into osteoblasts through the Wnt/β-catenin signaling pathway. At the same time, it may also inhibit the formation of osteoclasts mediated by RANKL.

IFRD1 regulates the asthmatic responses of airway via NF-κB pathway

Asthma is a chronic respiratory disease which is susceptible to children and causes great harm to them. Recently, Interferon-related developmental regulator 1 (IFRD1) was proved to be participant in regulating lung diseases, and its abnormal expression was shown in pathological airway tissues. Our study aimed to demonstrate the role and modulatory mechanism of IFRD1 in the pathogenesis of asthma. First, we evaluated the expression of IFRD1 in the lungs of asthmatic patients. C57BL/6 mice and human bronchial epithelioid (HBE) cells were respectively induced by ovalbumin (OVA) and lipopolysaccharide (LPS) to construct asthma models in vivo and in vitro. Using adenovirus and pcDNA vectors, we carried out overexpression assays on mice and cell models. Additionally, the potential mechanism of IFRD1 on regulating asthma process was elucidated by targeting NF-κB pathway. The results showed that IFRD1 was significantly down-regulated in asthma lung tissues, as well as the in vivo and in vitro models of asthma. Besides, OVA induced the inflammation responses and hyperreactivity of airway in mice, and LPS also caused inflammatory cytokine secretion and apoptosis of HBE cells, while cell viability was inhibited. However, IFRD1 overexpression dramatically reversed the effects of OVA and LPS. We subsequently discovered that the NF-κB pathway was activated in asthmatic cells, and NF-κB signaling activation was involved in IFRD1 regulated asthma responses of HBE cells. In conclusion, our study indicated that IFRD1 inhibited the asthmatic responses of airway via the NF-κB pathway inactivation. The evidence presented herein might provide a novel sight for asthma therapy.

Oridonin and its derivatives for cancer treatment and overcoming therapeutic resistance

Cancer is one of the diseases with high morbidity and mortality on a global scale. Chemotherapy remains the primary treatment option for most cancer patients, including patients with progressive, metastatic, and recurrent diseases. To date, hundreds of chemotherapy drugs are used to treat various cancers, however, the anti-cancer efficacy and outcomes are largely hampered by chemotherapy-associated toxicity and acquired therapeutic resistance. The natural product (NP) oridonin has been extensively studied for its anti-cancer efficacy. More recently, oridonin has been shown to overcome drug resistance through multiple mechanisms, with yet-to-be-defined bona fide targets. Hundreds of oridonin derivative analogs (oridonalogs) have been synthesized and screened for improved potency, bioavailability, and other drug properties. Particularly, many of these oridonalogs have been tested against oridonin for tumor growth inhibition, potential for overcoming therapeutic resistance, and immunity modulation. This concise review seeks to summarize the advances in this field in light of identifying clinical-trial level drug candidates with the promise for treating progressive cancers and reversing chemoresistance.

The matrix vesicle cargo miR-125b accumulates in the bone matrix, inhibiting bone resorption in mice

Communication between osteoblasts and osteoclasts plays a key role in bone metabolism. We describe here an unexpected role for matrix vesicles (MVs), which bud from bone-forming osteoblasts and have a well-established role in initiation of bone mineralization, in osteoclastogenesis. We show that the MV cargo miR-125b accumulates in the bone matrix, with increased accumulation in transgenic (Tg) mice overexpressing miR-125b in osteoblasts. Bone formation and osteoblasts in Tg mice are normal, but the number of bone-resorbing osteoclasts is reduced, leading to higher trabecular bone mass. miR-125b in the bone matrix targets and degrades Prdm1, a transcriptional repressor of anti-osteoclastogenic factors, in osteoclast precursors. Overexpressing miR-125b in osteoblasts abrogates bone loss in different mouse models. Our results show that the MV cargo miR-125b is a regulatory element of osteoblast-osteoclast communication, and that bone matrix provides extracellular storage of miR-125b that is functionally active in bone resorption.

MicroRNA-25-3p regulates osteoclasts through nuclear factor I X

Osteoporosis is a bone metabolic disease, characterized by loss of bone density leading to fractures. Its incidence increases with age and affects patient quality of life. Although osteoclasts play a significant role in osteoporosis, their underlying regulatory mechanisms remain unclear. In this study, we found that microRNA (miR)-25-3p negatively regulates osteoclast function through nuclear factor I X (NFIX). Overexpression of NFIX promoted osteoclast proliferation and increased the expression of the osteoclast differentiation and activity markers tartrate-resistant acid phosphatase and cathepsin K. MiR-25-3p transfection inhibited NFIX expression, which in turn inhibited osteoclast proliferation. Collectively, our results suggest that miR-25-3p promotes osteoclast activity by regulating the expression of NFIX. Therefore, targeting miR-25-3p in osteoclasts could be a promising strategy for treating skeletal disorders involving reduced bone formation.

A novel transgenic murine model with persistently brittle bones simulating osteogenesis imperfecta type I

Osteogenesis imperfecta (OI) type I caused by the null allele of COL1A1 gene is in the majority in clinical OI cases. Currently, heterozygous Mov-13 mice generated by virus insertion in the first intron of col1a1 is the exclusive model to modulate OI type I, in spite of the gradually recovered bone mineral and mechanical properties. A newly designed heterozygous col1a1^±365 OI mouse was produced in the present study by partial exons knockout (exon 2-exon 5, 365 nt of mRNA) using CRISPR/Cas9 system. The deletion resulted in generally large decrease in type I collagen synthesis due to frameshift mutation and premature chain termination, closely mimicking the pathogenic mechanism in affected individuals. And the strain possessed significantly sparse mineral scaffolds, bone loss, lowered mechanical strength and broken bone metabolism by 8 and 20 weeks compared to their littermates, suggesting a sustained skeletal weakness. Notably, the remarkable down-regulation of Yes-associated protein (YAP), one of the key coactivator in Hippo signaling pathway, was first found both in the femur and adipose derived mesenchymal stem cells (ADSCs) under osteogenic differentiation of col1a1^±365 mice, which might be responsible for the reduced osteogenic potential and brittle bones. Still, further research was needed in order to illuminate the underlying mechanism.

Chitooligosaccharide inhibits RANKL-induced osteoclastogenesis and ligation-induced periodontitis by suppressing MAPK/ c-fos/NFATC1 signaling

Considering the high rate of osteoclast-related diseases worldwide, research targeting osteoclast formation/function is crucial. In vitro, we demonstrated that chitooligosaccharide (CS) dramatically inhibited osteoclastogenesis as well as osteoclast function dose-dependently. CS suppressed osteoclast-specific genes expression during osteoclastogenesis. Furthermore, we found that CS attenuated receptor activator of nuclear factor kappa B ligand (RANKL)-mediated mitogen-activated protein kinase (MAPK) pathway involving p38, erk1/2, and jnk, leading to the reduced expression of c-fos and nuclear factor of activated T cells c1 (NFATc1) during osteoclast differentiation. In vivo, we found CS protected rats from periodontitis-induced alveolar bone loss by micro-computerized tomography and histological analysis. Overall, CS inhibited RANKL-induced osteoclastogenesis and ligature-induced rat periodontitis model, probably by suppressing the MAPK/c-fos/NFATc1 signaling pathway. Therefore, CS may be a safe and promising treatment for osteoclast-related diseases.

Octyl itaconate inhibits osteoclastogenesis by suppressing Hrd1 and activating Nrf2 signaling

The endogenous metabolite itaconate has emerged as a regulator of macrophage function that limits inflammation. However, its effect on cell differentiation and osteoclast-related diseases is unclear. Here, for the first time, we explored the effect of itaconate and its cell-permeable itaconate derivative, 4-octyl itaconate (OI) on osteoclast differentiation in vitro and in vivo. Firstly, we demonstrated that itaconate concentration was lower in estrogen-deficient mice. OI released itaconate and induced the expression of nuclear factor-erythroid 2-related factor 2 (Nrf2) in bone marrow-derived macrophages during osteoclastogenesis. Furthermore, OI significantly suppressed the early, middle, and late stages of osteoclastogenesis induced by receptor activator of NF-κB ligand in vitro, as confirmed by tartrate-resistant acid phosphatase staining. Moreover, it significantly inhibited fibrous actin ring formation and bone resorption in vitro. Mechanistically, we observed that OI enhanced Nrf2 expression by suppressing its association with ubiquitin via inhibition of the E3 ubiquitin ligase (Hrd1). OI also inhibited LPS-induced the reactive oxygen species and inflammatory responses via Hrd1. An estrogen deficiency (via ovariectomy)-induced osteoporosis model was also established. Here, on micro-computed tomography and histologic analysis showed that OI effectively suppressed ovariectomy-induced bone loss. In summary, OI, an itaconate derivative, can inhibit osteoclastogenesis in vitro and in vivo, indicating that OI could be a potential drug to treat osteoclast-related diseases; our results also link itaconate to the development of osteoporosis.-Sun, X., Zhang, B., Pan, X., Huang, H., Xie, Z., Ma, Y., Hu, B., Wang, J., Chen, Z., Shi, P. Octyl itaconate inhibits osteoclastogenesis by suppressing Hrd1 and activating Nrf2 signaling.

The Nrf2 activator RTA-408 attenuates osteoclastogenesis by inhibiting STING dependent NF-κb signaling

The dysregulation of ROS production and osteoclastogenesis is involved in the progress of osteoporosis. To identify novel and effective targets to treat this disease, it is important to explore the underlying mechanisms. In our study, we firstly tested the effect of the Nrf2 activator RTA-408, a novel synthetic triterpenoid under clinical investigation for many diseases, on osteoclastogenesis. We found that it could inhibit osteoclast differentiation and bone resorption in a time- and dose-dependent manner. Further, RTA-408 enhanced the expression and activity of Nrf2 and significantly suppressed RANKL-induced reactive oxygen species (ROS) production. Nrf2 regulates the STING expression and STING induces the production of IFN-β. Here, we found that RTA-408 could suppress STING expression, but that it does not affect Ifnb1 expression. RANKL-induced degradation of IκBα and the nuclear translocation of P65 was suppressed by RTA-408. Although this compound was not found to influence STING-IFN-β signaling, it suppressed the RANKL-induced K63-ubiquitination of STING via inhibiting the interaction between STING and the E3 ubiquitin ligase TRAF6. Further, adenovirus-mediated STING overexpression rescued the suppressive effect of RTA-408 on NF-κB signaling and osteoclastogenesis. In vivo experiments showed that this compound could effectively attenuate ovariectomy (OVX)-induced bone loss in C57BL/6 mice by inhibiting osteoclastogenesis. Collectively, we show that RTA-408 inhibits NF-κB signaling by suppressing the recruitment of TRAF6 to STING, in addition to attenuating osteoclastogenesis and OVX-induced bone loss in vivo, suggesting that it could be a promising candidate for treating osteoporosis in the future.

Administration of SB239063 Ameliorates Ovariectomy-Induced Bone Loss via Suppressing Osteoclastogenesis in Mice

Activation of osteoclast formation and function is crucial for the development of osteolytic diseases such as osteoporosis. RANKL (receptor activator of nuclear factor-κB ligand) activates NF-κB (nuclear factor κB), MAPK (mitogen-activated protein kinase), and NFATc1 (nuclear factor of activated T-cells, cytoplasmic 1) signaling pathways to induce osteoclastogenesis. In this study, we demonstrated that SB239063, a p38-specific inhibitor, suppressed osteoclastogenesis and bone resorption via inhibiting phosphorylation of MEF2C (myocyte enhancer factor 2C) and subsequently leading to MEF2C degradation by ubiquitination. Knockdown of MEF2C impaired osteoclast formation due to decreased c-Fos expression. Furthermore, MEF2C can directly bind to the promoter region of c-Fos to initiate its transcription. Interestingly, overexpression of either MEF2C or c-Fos can partially rescue the inhibitory effect of SB239063 on osteoclastogenesis. In addition, in vivo data proved that SB239063 also played a preventive role in both LPS (lipopolysaccharide)- and OVX (ovariectomy)-induced bone loss in mice. In conclusion, our results show that SB239063 can be a potential therapy for osteolytic diseases, and a novel p38/MEF2C/c-Fos axis is essential for osteoclastogenesis.

MicroRNA-200c Attenuates Periodontitis by Modulating Proinflammatory and Osteoclastogenic Mediators

This study tested whether microRNA (miR)-200c can attenuate the inflammation and alveolar bone resorption in periodontitis by using an in vitro and a rat model. Polyethylenimine (PEI) was used to facilitate the transfection of plasmid DNA encoding miR-200c into primary human gingival fibroblasts (HGFs) and gingival tissues of rats. We first analyzed how proinflammatory and osteoclastogenic mediators in HGFs with overexpression of miR-200c responded to Porphyromonas gingivalis lipopolysaccharide (LPS-PG) challenge in vitro. We observed that overexpression of miR-200c significantly reduced interleukin (IL)-6 and 8 and repressed interferon-related developmental regulator-1 (IFRD1) in HGFs. miR-200c also downregulated p65 and p50. In a rat model of periodontitis induced by an LPS injection at the gingival sulcus of the second maxillary molar (M2), we analyzed how the mediators in rat gingiva and alveolar bone resorption responded to miR-200c treatment by a local injection of PEI-plasmid miR-200 nanoplexes. We observed that the local injection of miR-200c significantly upregulated miR-200c expression in gingiva and reduced IL-6, IL-8, IFRD1, and the ratio of receptor activator of nuclear factor kappa-B ligand/osteoprotegerin. Using micro-computed tomography analysis and histomorphometry, we further confirmed that local treatment with miR-200c effectively protected alveolar bone resorption in the rat model of periodontitis by reducing the distance between the cemento-enamel junction and the alveolar bone crest and the inter-radicular space in the upper maxilla at M2. These findings imply that miR-200c may serve as a unique means to prevent periodontitis and associated bone loss.

LY411575, a potent γ-secretase inhibitor, suppresses osteoclastogenesis in vitro and LPS-induced calvarial osteolysis in vivo

A series of osteolytic bone diseases are usually related to excessive bone resorption and osteoclast formation. Thus, agents or drugs which can target osteoclast development and attenuate bone loss are potentially considerable in preventing and treating of bone lytic diseases. In recent years, many studies have reported that Notch signaling has substantial impacts on the process of osteoclast differentiation, maturation, and bone destruction. In the present study, we showed that LY411575, a γ-secretase inhibitor, could potently suppress osteoclast differentiation, osteoclast-specific gene expression, and bone resorption via suppressing Notch/HES1/MAPK (ERK and p38)/Akt-mediated NFATc1 induction in vitro. Consistent with in vitro results, LY411575 exhibited protective effects in lipopolysaccharides-induced calvarial bone destruction in vivo. Collectively, these results indicate that LY411575 may have therapeutic potential in the treatment of osteoclast-mediated osteolytic bone diseases.

Macrophage migration inhibitory factor (MIF) inhibitor 4-IPP suppresses osteoclast formation and promotes osteoblast differentiation through the inhibition of the NF-κB signaling pathway

Current pharmacological intervention for the treatment of osteolytic bone diseases such as osteoporosis focuses on the prevention of excessive osteoclastic bone resorption but does not enhance osteoblast-mediated bone formation. In our study, we have shown that 4-iodo-6-phenylpyrimidine (4-IPP), an irreversible inhibitor of macrophage migration inhibitory factor (MIF), can inhibit receptor activator of NF-κB ligand (RANKL)-induced osteoclastogenesis and potentiate osteoblast-mediated mineralization and bone nodule formation in vitro. Mechanistically, 4-IPP inhibited RANKL-induced p65 phosphorylation and nuclear translocation by preventing the interaction of MIF with thioredoxin-interacting protein-p65 complexes. This led to the suppression of late osteoclast marker genes such as nuclear factor of activated T cells cytoplasmic 1, resulting in impaired osteoclast formation. In contrast, 4-IPP potentiated osteoblast differentiation and mineralization also through the inhibition of the p65/NF-κB signaling cascade. In the murine model of pathologic osteolysis induced by titanium particles, 4-IPP protected against calvarial bone destruction. Similarly, in the murine model of ovariectomy-induced osteoporosis, 4-IPP treatment ameliorated the bone loss associated with estrogen deficiency by reducing osteoclastic activities and enhancing osteoblastic bone formation. Collectively, these findings provide evidence for the pharmacological targeting of MIF for the treatment of osteolytic bone disorders.-Zheng, L., Gao, J., Jin, K., Chen, Z., Yu, W., Zhu, K., Huang, W., Liu, F., Mei, L., Lou, C., He, D. Macrophage migration inhibitory factor (MIF) inhibitor 4-IPP suppresses osteoclast formation and promotes osteoblast differentiation through the inhibition of the NF-κB signaling pathway.

Vitexin suppresses RANKL-induced osteoclastogenesis and prevents lipopolysaccharide (LPS)-induced osteolysis

Osteolytic diseases are characterized by an increase in the number and/or activity of bone-resorbing osteoclasts. Identification of natural compounds that can suppress osteoclast formation and function is crucial for the prevention and treatment of osteolytic diseases. Vitexin, a naturally-derived flavonoid extracted from various medicinal plant species, demonstrates a broad range of pharmacological properties including anticancer and anti-inflammatory effects. Here in this study, we showed that vitexin exerts antiosteoclastogenic effects by directly inhibiting receptor activator of nuclear factor-κB ligand (RANKL)-induced osteoclast formation and bone resorption in vitro and protected against lipopolysaccharide (LPS)-induced inflammatory osteolysis in vivo. Vitexin suppressed the early activation of ERK and p38 MAPK pathways in response to RANKL thereby attenuating the downstream induction of c-Fos and NFATc1, and abrogating the expression of osteoclast marker genes. Collectively, these results provide evidence for the therapeutic application of vitexin in the treatment of osteoclast-mediated bone lytic diseases.

SREBP-2 aggravates breast cancer associated osteolysis by promoting osteoclastogenesis and breast cancer metastasis

Bone is one of the most common sites of breast cancer metastasis and a major cause of high mortality in these patients. Thus, further understanding the molecular mechanisms regulating breast cancer-induced osteolysis is critical for the development of more effective treatments. In this study, we demonstrated that important roles sterol regulatory element-binding protein 2 (SREBP-2) play in osteoclast formation a function, and in breast cancer metastasis. SREBP-2 expression was found to be induced during the early stages of osteoclast formation under the control of the RANKL/cAMP-response element binding protein (CREB) signaling cascade. SREBP-2 is subsequently translocated into the nucleus where it participates with other transcriptional factors to induce the expression of NFATc1 required for mature osteoclast formation. Additionally, SREBP-2 was also found to be highly expressed in breast cancer tissues and correlated with a poor prognosis. SREBP-2 was similarly under the transcriptional control of CREB and its induction regulates the expression of matrix metalloproteinases (MMPs), key degradative enzymes involved in bone metastases by breast cancer cells. Accordingly, targeting of SREBP-2 with Fatostatin which specifically inhibits SCAP (SREBP cleavage-activating protein) and prevents SREBP activation, attenuated breast cancer-induced osteolysis in vivo. Collectively, our results suggest that SREBP-2 plays a critical role in regulating osteoclastogenesis and contributes to breast cancer-induced osteolysis. Thus, SREBP-2 inhibition is a potential therapeutic approach for breast cancer patients with osteolytic bone lesions.

Activating β-catenin/Pax6 axis negatively regulates osteoclastogenesis by selectively inhibiting phosphorylation of p38/MAPK

Balance of osteoclast formation is regulated by the receptor activator of NF-κB ligand and extracellular negative regulators such as IFN-γ and IFN-β. However, very little is known about the intrinsic negative regulatory factors of osteoclast differentiation. Recently, the paired-box homeodomain transcription factor Pax6 was shown to negatively regulate receptor activator of NF-κB ligand-mediated osteoclast differentiation. However, the mechanism underlying this regulation is still unclear. In this study, we show that a p38 inhibitor (VX-745) up-regulates the expression of Pax6 during osteoclast differentiation. Subsequently, we found that β-catenin could bind to the proximal region of Pax6 promoter to induce its expression, and this action could be impaired by p38-induced ubiquitin-mediated degradation of β-catenin. Our results suggest that Pax6 is regulated by a novel p38/β-catenin pathway. Pax6 can further regulate the nuclear translocation of NF of activated T cells, cytoplasmic 1. Our study indicates that this novel p38/β-catenin/Pax6 axis contributes to negative regulation of osteoclastogenesis. In addition, our study proposes a novel approach to treat osteoclast-related diseases through the use of VX-745 complemented with the β-catenin activator SKL2001.-Jie, Z., Shen, S., Zhao, X., Xu, W., Zhang, X., Huang, B., Tang, P., Qin, A., Fan, S., Xie, Z. Activating β-catenin/Pax6 axis negatively regulates osteoclastogenesis by selectively inhibiting phosphorylation of p38/MAPK.

Rubiadin-1-methyl ether from Morinda officinalis How. Inhibits osteoclastogenesis through blocking RANKL-induced NF-κB pathway

Rubiadin-1-methyl ether (RBM) is a natural anthraquinone compound isolated from the root of Morinda officinalis How. In our previous study, RBM was found to have inhibitory effects on the TRAP activity of osteoclasts, which means that RBM may be a candidate for therapy of bone diseases characterized by enhanced bone resorption. However, the further effect of RBM on osteoclasts and the underlying mechanism remain unclear. In the present study, we investigated the effects of RBM isolated from Morinda officinalis How. on osteoclasts derived from bone marrow macrophages (BMMs) and the underlying mechanism in vitro. RBM at the dose that did not affect the viability of cells significantly inhibited RANKL-induced osteoclastogenesis and actin ring formation of osteoclast, while RBM performed a stronger effect at the early stage. In addition, RBM downregulated the expression of osteoclast-related proteins, including nuclear factor of activated T cells cytoplasmic 1 (NFATc1), cellular oncogene Fos (c-Fos), matrix metallopeptidase 9 (MMP-9) and cathepsin K (CtsK) as shown by Western blot. Furthermore, RBM inhibited the phosphorylation of NF-κB p65 and the degradation of IκBα as well as decreased the nuclear translocation of p65. Collectively, the results suggest that RBM inhibit osteoclastic bone resorption through blocking NF-κB pathway and may be a promising agent for the prevention and treatment of bone diseases characterized by excessive bone resorption.

A novel anti-osteoporotic agent that protects against postmenopausal bone loss by regulating bone formation and bone resorption

AIMS

Postmenopausal osteoporosis is a bone metabolism disease that is caused by an imbalance between bone-resorbing osteoclast and bone-forming osteoblast actions. Herein, we describe the role of troxerutin (TRX), a trihydroxyethylated derivative of rutin, in ovariectomy (OVX)-induced osteoporosis and its effects on the regulation of osteoclasts and osteoblasts.

MAIN METHODS

In vivo, OVX female mice were intraperitoneally injected with either saline, 50 mg/kg TRX, or 150 mg/kg TRX for 6 weeks and then sacrificed for micro-computed tomography analyses, histological analyses, and biomechanical testing. In vitro, RAW264.7 cell-derived osteoclasts and MC3T3-E1 cell-derived osteoblasts were treated with different concentrations of TRX to examine the effect of TRX on osteoclastogenesis and bone resorption, as well as on osteogenesis and mineralization.

KEY FINDINGS

In this study, we demonstrated that TRX prevented cortical and trabecular bone loss in ovariectomized mice by reducing osteoclastogenesis and promoting osteogenesis in vivo. In vitro, TRX inhibited the formation and activity of RAW264.7-derived osteoclasts and the expression of nuclear factor of activated T-cells 1 and cathepsin K. Meanwhile, TRX improved the osteogenesis and mineralization of MC3T3-E1 by enhancing the expression of Runt-related transcription factor 2, Osterix, and collagen type 1 alpha 1.

SIGNIFICANCE

Our data demonstrated that TRX could prevent OVX-induced osteoporosis and be used in a novel treatment for postmenopausal osteoporosis.

Cepharanthine Prevents Estrogen Deficiency-Induced Bone Loss by Inhibiting Bone Resorption

Osteoporosis is a common health problem worldwide caused by an imbalance of bone formation vs. bone resorption. However, current therapeutic approaches aimed at enhancing bone formation or suppressing bone resorption still have some limitations. In this study, we demonstrated for the first time that cepharanthine (CEP, derived from Stephania cepharantha Hayata) exerted a protective effect on estrogen deficiency-induced bone loss. This protective effect was confirmed to be achieved through inhibition of bone resorption in vivo, rather than through enhancement of bone formation in vivo. Furthermore, the in vitro study revealed that CEP attenuated receptor activator of nuclear factor κB ligand (RANKL)-induced osteoclast formation, and suppressed bone resorption by impairing the c-Jun N-terminal kinase (JNK) and phosphatidylinositol 3-kinase (PI3K)-AKT signaling pathways. The inhibitory effect of CEP could be partly reversed by treatment with anisomycin (a JNK and p38 agonist) and/or SC79 (an AKT agonist) in vitro. Our results thus indicated that CEP could prevent estrogen deficiency-induced bone loss by inhibiting osteoclastogenesis. Hence, CEP might be a novel therapeutic agent for anti-osteoporosis therapy.